The effect of various factors, including disease and protein concentration, on the binding of drugs to plasma albumin has been investigated. The binding of several acidic drugs to albumin from uremic and neonatal subjects was reduced. While there were differences in the amino acid composition of albumin from uremics and neonates, no differences in their immunological properties were observed. Isoelectric focussing separates normal albumin into two components with isoelectric points of 4.8 and 5.0. Both the uremic and the neonatal albumins had differing amounts of these two components when compared to normal albumin. The reduction in drug binding observed when albumin concentration is increased is not due to polymerization of the protein but may result from a change in protein conformation. BIBLIOGRAPHIC REFERENCES: Wallace, S. (Boobis, S.W.): Altered plasma albumin in relation to the newborn infant. Br. J. Clin. Pharmac. 4: 82-85, 1977. Chignell, C.F.: Protein binding. In Hirtz, J.L. and Garrett, E.R. (Eds.): Drug Fate and Metabolism: Methods and Techniques. New York, Marcel Dekker Inc., 1977, vol. 2, pp. 87-228.